1. Field of the Invention
This invention relates to electronic data processing apparatus. More specifically, it relates to means responsive to signals being transmitted between a computer and a display unit having a keyboard for measuring the response time of the computer, that is, the time required for completion of a computer activity.
2. Discussion of the Prior Art
Many forms of data processing systems are known in the art which include data input equipment, a central processor, a memory and output devices, such as printers, punches, memories, and the like. In these systems, data which is either stored in the system or entered into the system by an operator, for example by a keyboard, is manipulated in accordance with predetermined programs, and then the completed work is displayed visually or in a printout or otherwise recorded for later use. In large scale systems of this general type, use is frequently made of terminals, placed in different locations for the convenience of the user, by means of which many different users can have access to the computer for the performance of the variety of data processing operations which may be programmed into the computer. Because of the high cost of acquiring and operating computer equipment, it is desirable for the organization using the computer to have accurate cost information regarding the time that it takes the computer to perform each operation fo each different user in order to enable the organization to allocate and control the cost of using the equipment most effectively.
For this purpose, it is desirable to know the actual operating or response time the computer takes to complete a particular process. This information should be made available at the computer terminal, as part of the information displayed, or as a printout, when such is needed.
The need for computer process time measurement capabilities of the type discussed above has been recognized in the computer industry and arrangements in which operation of timing circuitry in the computer is controlled by programmed instructions are known.
There is a need, however, for a simple, inexpensive auxiliary equipment which can be added to existing systems for performing this function.
One auxiliary system is known, which may be attached to a computer and which depends for its operation on the "system available" status symbol which is flashed on the viewing screen of the terminal when a particular operation is completed. The "system available" or "system inhibit" signals used in a display terminal are usually in the nature of a spot and may, for example, be made up of several horizontal lines of the video raster having a length equal to the width of an alphabet character, which appear at a location on the right hand side of the screen. In the prior art auxiliary system, a photoelectric cell is applied to the face of the cathode ray tube to detect the light from the status symbol. When the symbol is detected, a microprocessor, separate from the computer being measured, processes the signal from the photocell. For such processing it may be necessary to compensate for variations in the signal strength resulting from the software used, for scan characteristics, for changeable refresh rates, for spot brightness and duration, and for other system characteristics which influence the brightness of the spot. This system is complex and its performance is easily affected by failure to compensate precisely for the system variables just mentioned.
It is an object of the present invention to use one or more signals generated by a computer for measuring the time it takes the computer to complete a particular operation.
Another object of the invention is to provide a reliable and convenient system of measurement for use at a computer terminal which is also capable of supplying the information generated to the central processor.